Use python 3 for release tools

The release tools have already been updated in prior cls to
support python 3. To test this, I added code to print the script
name to a temp file at the beginning of every script, and then
ran various builds, ensuring that the scripts were run afterwards.

The builds run:
m brillo_update_payload checkvintf minigzip lz4 toybox unpack_bootimg deapexer (needed for releasetools_test)
m (as both sdk_phone_x86_64 and beagle_x15)
m target-files-package (as both sdk_phone_x86_64 and beagle_x15)
m releasetools_test && out/host/linux-x86/nativetest64/releasetools_test/releasetools_test (25 errors with and without python3)
m check_target_files_signatures apksigner target-files-package && out/host/linux-x86/bin/check_target_files_signatures out/target/product/emulator_x86_64/obj/PACKAGING/target_files_intermediates/sdk_phone_x86_64-target_files-eng.colefaust.zip
m dist
As aosp_cf_x86_64_phone: m dist && sign_target_files_apks  out/dist/aosp_cf_x86_64_phone-target_files-eng.$USER.zip /tmp/signed_target_files.zip && validate_target_files /tmp/signed_target_files.zip

This hit all the scripts except for make_recovery_patch,
merge_builds, and ota_package_parser.

I couldn't find anything that uses merge_builds, so it must
only be run manually.

make_recovery_patch and ota_package_parser are only run if
TARGET_OTA_ALLOW_NON_AB is true (among other things), which
is not the case for any product in aosp.

Test: Described in commit message + presubmits
Change-Id: I1a29eafa7ff1a69973b27055e311de77f7ee628b